1. Field Of The Invention
This invention relates to a three-dimensional viewing system and, in particular, to a system permitting viewing of left and right stereoscopic images by a plurality of observers.
2. Brief Statement Of The Prior Art
A system for three-dimensional imaging of optical images was invented almost 150 years ago. In 1849, the system was improved by Brewster who used a pair of solid wedge prisms, and refined further by Holmes, who added a pair of convex lens eyepieces, giving birth to the popular stereoscope, in which a hooded eyepiece was provided with left and right prismatic lenses of short focal length, and a central rail with a wooden slide to hold left and right stereoscopic photographic images. One focused the images by moving the slide toward, or away from, one's eyes. This stereoscope has not been improved upon for the past 75 years. While this stereoscope provided a single viewer with enjoyable three-dimensional viewing, it has not found other applications because it is limited to viewing by a single observer and because it requires the use of photographic images which must be manually inserted into the slide holder.
Sheiman and Rudell in U.S. Pat. Nos. 4,235,515 and 4,422,720 describe stereoscopic image display utilizing one or two Fresnel prisms. These systems, however, are best suited for viewing by one or two observers, and require display of left and right images at ninety degrees to each other, thus restricting usage and complicating monitor displays. These systems also are not readily adaptable to display of large images. Discrimination by an observer of each stereoscopic image is achieved by light refraction or reflection, resulting in critical positioning of the observer for correct viewing.
Swan, in U.S. Pat. No. 51,906 issued in 1866 discloses a stereoscopic image display using two, solid core, right angle prisms. This system has the same limitations as the aforementioned Sheiman and Rudell patents and, additionally is very bulky and cumbersome and further greatly limits the size of the images. This system is entirely incompatible with single monitor (CRT) display.
Baumgardner, in U.S. Pat. No. 3,972,596, describes use of a flat Fresnel lens for image magnification or compression, as in a wide angle lens application. Baumgardner's employment of Fresnel optics is for one image, only without any suggestion of image pairs for any purpose, particularly stereoscopy.
Prior stereoscopic systems have used right and left image coding with polarized or monochromatic-color light and eyepieces having polarized or colored filters worn by the observers. In all past systems, however, it has been necessary to encode the images at their projection site and to use a special screen to maintain polarity of the displayed images. These requirements have prevented application to electronic image display, e.g., television, since polarization cannot be achieved or maintained during electronic transmission or monitor display. Additionally, the stereoscopic images have typically been superimposed over each other at the point of final display and separate polarization of each image has to be performed prior to the superimposition and then maintained throughout transmission to the point of final display to a viewer or viewers. While this is acceptable in a movie theater, where polarizing elements can be positioned in front of a projection device and the separate images can undergo polarization as they pass through the elements and onto a special screen which maintains polarization, it has precluded applications in telephonic, fiber optic and electronic image transmission and broadcasting.